China's Foreign Ministry on Friday strongly criticized Japan after a Self-Defense Forces (SDF) vessel transited the Taiwan Strait, warning that the Taiwan question is a "red line" that must not be crossed.

Foreign Ministry spokesperson Guo Jiakun made the remarks at a press briefing. He said the Chinese military had "handled the situation in accordance with laws and regulations" after the Japanese vessel entered the strait earlier that day. He accused the Japanese government of showing off force and engaging in deliberate provocation, describing the move as "a mistake compounded."

Guo said that Japanese Prime Minister Sanae Takaichi's remarks on China's Taiwan region at the end of last year had already dealt a serious blow to China-Japan relations. The latest naval activity, he added, further exposed "dangerous intentions" among some in Japan to interfere militarily in the Taiwan Strait and undermine regional stability.

"The Taiwan question concerns China's sovereignty and territorial integrity and forms the political foundation of China-Japan relations. It is an insurmountable red line," Guo said. He noted that China has lodged strong protests with Japan and urged it to "reflect on its actions, correct its mistakes and refrain from going further down the wrong path."

Amid ongoing strained China-Japan relations, discriminatory incidents targeting Chinese nationals in Japan have risen markedly. Just one week after an active-duty SDF officer forced his way into the Chinese embassy in Tokyo wielding a knife, another individual claiming to belong to the SDF's emergency reserve issued a terrorist threat in an online video, alleging that a remotely controlled bomb had been planted at the embassy.

According to Guo, these incidents highlight deeper issues within Japan, including the rise of right-wing sentiment, inadequate historical education, and a shift in Japan's security policy toward a more "aggressive, expansionist and risky" posture. He also criticized Japan's lapses in oversight and discipline within the SDF.

"How to fundamentally address these problems is a question worthy of serious reflection by those in Japan with insight," Guo said, warning that downplaying such incidents or deflecting responsibility could lead to more severe consequences.

"We once again urge Japan to conduct thorough reflections and investigations, make corrections and provide a responsible explanation to China," said Guo.